Preston, I'm not sure I understand your question but I will give it a try. Most thermostats that I have seen have Cool /Heat on one switch and Auto / Fan on the other. If you set it to Fan, the blower motor runs constantly, whereas in Auto, it will cycle when either the AC or Furnace comes on.
Your original having High/Low gives you some additional control, which is why you see folks adding a micro switch to their installs when changing out the thermostat for a digital model.
Mike, Sue, Sissy and Little Man
2015 Ford F350 Lariat FX4 6.7 CC DRW
2015 Eagle Premier 351RSTS